Infernal Affairs (Mou Gaan Dou)

Andy Lau was recruited by a gangster boss as a teenager, sent into Hong Kong’s police academy to be a mole within the ranks and help keep criminal business prosperous. Tony Leung was expelled from police training as a young man as part of a covert operation to send him behind the lines and be a mole among the criminals. Both sides become suspicious of espionage amongst them and send each of these guys in search of the other spy, their lives criss-crossing amidst a series of increasingly tense and exciting action sequences. Intelligent and slick, this is a superb action film with just enough character depth to make it matter without ever being weighed down by too much drama. Its success inspired two sequels and was later remade by Martin Scorsese as the Oscar-winning crime epic The Departed.